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Re: Thanks, Rob, might be idle mixture... (archive)
[ Follow Ups ] [ 5-series (E28) Message Board ] [ Msg. Board FAQ ]
Posted by Rob Anderson on March 18, 2001 at 21:53:53:

In Reply to: Thanks, Rob, might be idle mixture... posted by Clyde on March 18, 2001 at 12:57:48:

Yes mine is discolored a little. I would be very surprised that your O2 sensor is still good. I personally do not have the readings it should be giving maybe someone else can provide you with these. I would try to do the unplug the ECU and re plug it in trick. That might help.

Rob
M535i SIG Chief Technical Advisor
www.m535i.org

The converter itself is in good physical shape (no dings). The bottom half has a bluish-purple patina -- don't know if that's normal or whether it is a sign of overheating. If yours isn't discolored then maybe a rich idle condition has been stressing the catalyst, and your tip about the CO idle adjustment would be a good place to begin.

However, I'm not sure how to adjust idle mix on this car without a CO meter. Could I use the O2 sensor (disconnected from the Motronic) as an indicator? What voltage signature should I aim for -- is it feasible to achieve a setting where sensor voltage "hunts" or should I set it for slightly lean (just below 0.5 V)? Or should I give this to a shop to do?

It's been 23,000 miles since last tuneup, so before I check the idle mix, I will adjust the valves and replace the plugs. maybe that's the culprit for the short catalyst life.

Lastly, here are the CA emissions limits for the 15 mph and 25 mph dyno tests (they no longer look at idle, but run the cars with a load to the drivetrain); looking at my results, the manager of a "test-only" station suggested that the measured results looked like the car was running with a good fuel/air ratio but with an ineffective cat:

15 mph 25 mph
%CO2 (info only) 14.2 14.7
%O2 (info only) 0.5 0.1

HC (ppm)
max allowed 133 83
gross polluter limit 283 233
my test result 125 51

CO (pct)
max allowed .71 .58
gross polluter limit 2.21 2.08
my test result .50 .22

NO (ppm)
max allowed 1020 880
gross polluter limit 1957 1757
my test result 2399 971




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